1. Field
The present disclosure relates to a receiver for receiving signals communicated via proximity communication. More specifically, the present disclosure relates to a receiver that includes adaptive offset compensation and decision feedback.
2. Related Art
Proximity communication is an input/output (I/O) technology that allows chips to communicate through capacitive signaling. Although proximity communication can potentially provide much higher I/O density and lower power consumption, detecting signals that are communicated using proximity communication can be challenging. In particular, signals coupled onto proximity connectors or nodes of a receiving chip can be very small (on the order of 1 mV). Furthermore, because capacitors block DC voltages, the receiving nodes often need to be biased to appropriate DC levels.
Furthermore, detecting small signals over a capacitively coupled interface can pose significant challenges in the design of fast, reliable data receivers. For example, input offset(s) subtract from the received signal, which degrades receiver sensitivity. Therefore, for robust communication, offset cancellation is typically used, especially in advanced fabrication processes in which transistor-mismatch effects are more significant.
In addition, the input nodes of amplifiers on the receiving chip typically need to be biased to voltage levels where the amplifiers have adequate gain. One existing technique for solving this problem uses a transistor in sub-threshold operation to slowly bias a floating node. In this case, the source, body, and gate terminals are all coupled to a bias voltage, such that the transistor is off and the node is biased using the transistor's leakage current. However, in this technique a minimum transition frequency in the incoming signal is usually needed. Otherwise, all of the nodes will eventually drift toward the bias voltage, and the signal will be erased. Furthermore, if the signal is not DC-balanced, the DC levels on the two terminals of a differential amplifier may also drift apart, which reduces the voltage margin. As a consequence, this existing technique typically imposes restrictions on the data pattern through the channel, which often can only be ensured by performing coding at a higher level.
In another existing technique for biasing the amplifiers on the receiving chip, the floating nodes are biased by periodically ‘refreshing’ all channels. For example, every so often, the channels are stopped, and all the floating nodes are pre-charged to the appropriate bias levels. However, because this technique requires that communication be stopped at periodic intervals while the refresh occurs, significant architectural complexities can be introduced into systems. Alternatively, extra communication channels may be used, and data channels may be rotated to these extra channels while the data channels are being refreshed. While this approach can hide the complexity of the refresh mechanism from the overall system architecture, it requires precise coordination between the transmitting and receiving chips to ensure proper synchronization of the refresh channels, which can be difficult and expensive to implement.
Hence, what is needed is a circuit which receives signals communicated via proximity communication without the above-described problems.